Metal halide arc discharge lamps may have high luminous efficacy and long life and may be employed in commercial usage. In one embodiment, a metal halide arc discharge lamp may include a quartz or fused silica arc tube that is hermetically sealed within a borosilicate glass outer envelope. The arc tube, itself hermetically sealed, may have tungsten electrodes sealed into opposite ends and may contain a fill material including mercury, metal halide additives and/or a rare gas to facilitate starting. In some cases, e.g. in high wattage lamps, the outer envelope may be filled with nitrogen or another inert gas at less than atmospheric pressure. In other cases, e.g. in low wattage lamps, the outer envelope may be evacuated.
Metal halide lamps may be configured to start upon application of a high voltage between two main electrodes or to an inductive start system. Metal halide lamps which do not contain UV enhancers may require higher voltage pulses to release avalanche initiating electrons. Initiating electrons, in this manner, are believed to be released from the electrode by field emission or by field extraction from charges in shallow traps on the wall of the arc tube. However, not all sockets into which such lamps are inserted have the capacity to carry the high voltage needed to start the lamps.
Accordingly, a starting aid, also known as an ultraviolet enhancer (UVE), may be provided in such lamps. In one embodiment, a conventional UVE may include a capsule with a sealed cavity that may contain a gas or a mixture of gases, such as mercury vapor and an inert gas (argon, helium, krypton, neon, or xenon). An electrode may extend into the cavity and may provide a voltage from one of the discharge vessel electrodes. Upon application of the starting voltage, a capacitive discharge may start in the capsule and may cause the capsule to emit UV radiation, which in turn may cause the release of photoelectrons in the lamp, which in turn may lower the voltage needed to start the lamp.
In one embodiment, a metal halide lamp may include a discharge vessel in an outer bulb. The discharge vessel may have two electrodes that receive the voltage for starting the lamp. The UVE may be located within the outer bulb and connected to one of the electrodes. The UVE may be positioned close to the other electrode to allow capacitive coupling. A gas inside the UVE may be partially ionized by the capacitive coupling and may emit UV light that aids in starting the lamp.
In some applications, it may be desirable to provide a holding means configured to hold the UVE in a particular position within the lamp. Examples of lamps utilizing such holding means may be found, for example, in EP 2151850 A2 (Ishida), U.S. Patent Pub. No. 2008/0169744 (Fortuna); U.S. Pat. No. 6,392,343 (Luijks); U.S. Pat. No. 5,248,273 (Nortrup); U.S. Pat. No. 5,122,706 (Parrot); and U.S. Pat. No. 4,818,915 (Zaslaysky).
FIG. 1 is a side view of an exemplary metal halide discharge lamp including a UVE held in position within the lamp by a prior art holding means. Generally, the metal halide discharge lamp 100 may include a lamp envelope 102 and a base 104 fixed at one end of the envelope 102. As shown, the base 104 may be formed for easy connection to an electrical source. Contained within the interior space of the lamp envelope 102 is a mount assembly. The mount assembly may include a light source, lamp capsule, or arc tube 106, a shroud 108, and a mounting frame 110. In the illustrated embodiment, the arc tube 106 may be positioned within the shroud 108, wherein the arc tube 106 and shroud 108 may be supported within the envelope 102 by the mounting frame 110.
As shown, the arc tube 106 may include first and second electrodes 112, 114. The mounting frame 110 may be non-insulated and electrically conductive and may serve as a first electrical lead, wherein a first conductive wire 116 may electrically connect a portion of the electrically conductive mounting frame 110 to the first electrode 112 of the arc tube 106. Additionally, a second conductive wire 118 may electrically connect the second electrode 114 of the arc tube 106 to a second lead 120. A portion of the mounting frame 110 and the second lead 120 pass through a lamp stem portion 122 at the base 104.
As shown, the electrically conductive mounting frame 110 and the second lead 120 are electrically connected to the base 104 external of the envelope 102 and are configured to provide energization of the lamp 100, specifically the arc tube 106. In other words, electrical energy may be coupled to the arc tube 106 through the base 104, second lead 120, mounting frame 110 and first and second conductive wires 116, 118. The arc tube 106 may contain a chemical fill or dose of materials to provide light when an arc is initiated therein, as is known.
The lamp 100 may further include a starting aid, or UVE 124, disposed within the lamp envelope 102. The UVE 124 may be electrically connected to at least the second lead 120 of the lamp 100 via a UVE electrical lead 126 extending from the UVE 124. Additionally, the lamp 100 may include a holding means 128 configured to hold the UVE 124 in a desired position within the lamp envelope 102, wherein a portion of the holding means 128 is coupled to a portion of the mounting frame 110.
FIG. 2 is an enlarged partial side view of the lamp of FIG. 1 showing the UVE 124 held in position by the prior art holding means 128 and FIG. 3 is a sectional view taken along line 3-3 of FIG. 2. Referring to FIG. 2, the UVE 124 may include an envelope 230 and an electrode 232 sealed within the envelope 230. The electrode 232 may be coupled to the UVE electrical lead 126, and coupled to the second lead 120. Other details relating to the UVE 124 are disclosed in at least the '915 patent identified above. Referring to FIGS. 2 and 3, the prior art holding means 128 may include a single strip of metal foil wrapped around the envelope 230 of the UVE 124. The foil strip 128 may include a first leg 234 and a second leg 236 disposed at opposite ends of the strip 128. During manufacturing, at least the first leg 234 of the foil strip 128 is coupled to a portion of the mounting frame 110 by a first weld 238. Additionally, in order to hold the UVE 124, the foil strip 128 may include a flexible material, such as nickel, thereby allowing the strip 128 to be bent and shaped around the UVE 124. Upon wrapping the foil strip 128 around the UVE 124, the second leg 236 may be coupled to a portion of the foil strip 128 by a second weld 240 in order to secure the UVE 124.
In many applications, it may be desirable for the UVE to be securely and accurately placed in a certain position within a metal halide lamp. The current UVE holding means, such as the foil strip described above, have flaws in structure and/or function. For example, in regards to the foil strip described above, during manufacturing, the required close proximity of the foil strip around the glass envelope of the UVE may result in glass damage and/or breakage when the strip is wrapped around the UVE. Additionally, construction of the UVE foil strip holder may require at least two coupling points, such as the first and second welds. This may increase assembly time and manufacturing costs, as well as chance of error with regard to welding points.